1. Field of the Invention
The present invention relates generally to a semiconductor device such as a thin film transistor, and more particularly, to a thin film transistor in which internal stress is relaxed in the interfaces of a semiconductor thin film serving as an active layer and insulator films.
2. Description of the Prior Art
A thin film transistor (hereinafter referred to as TFT) using amorphous, polycrystalline, microcrystalline semiconductors or a semiconductor obtained by mixing these semiconductors in place of a conventional single crystal semiconductor has been developed. The semiconductor materials listed as described above are hereinafter collectively referred to as non-single crystal semiconductors in the present invention.
Of the non-single crystal semiconductors, an amorphous semiconductor material, particularly amorphous silicon (hereinafter abbreviated as a-Si) is frequently used when TFTs are formed in large quantities on a substrate having a large area from the advantages that its characteristics of semiconductor as a transistor are stable and a-Si having a large area can be formed.
Such a TFT also utilizes the advantages that a semiconductor thin film having a large area can be easily formed in the plasma CVD (chemical vapor deposition) method and at the same time, a silicon nitride (hereinafter abbreviated as SiN.sub.x) film to be a gate insulator film or a passivation film which constitutes the TFT can be continuously formed by only changing source gases in the same method.
In the above described TFT, SiN.sub.x insulator films for a gate insulator film and a passivation film are provided with a semiconductor thin film serving as an active layer being sandwiched therebetween, as described in an article entitled "Reactive Plasma Deposited Si-N Films for MOS-LSI Passivation", J. Electrochem. Soc. "SOLID-STATE SCIENCE AND TECHNOLOGY", April 1978 and an article entitled "Gate dielectric and contact effects in hydrogenated amorphous silicon-silicon nitride thin-film transistors", J. Appl. Phys., Vol. 65, No. 10, May 15, 1989. Such a TFT has the disadvantage in that internal stress is produced by the difference in material between the semiconductor thin film and the SiN.sub.x insulator films, and cracking occurs in the SiN.sub.x insulator films or the semiconductor thin film by the internal stress in the fabricating processes of the TFT.